[pve-devel] [PATCH kernel] cherry-pick fix for CVE-2016-4470

Fabian Grünbichler f.gruenbichler at proxmox.com
Wed Jul 13 15:28:14 CEST 2016


---
 ...470-KEYS-potential-uninitialized-variable.patch | 94 ++++++++++++++++++++++
 Makefile                                           |  1 +
 2 files changed, 95 insertions(+)
 create mode 100644 CVE-2016-4470-KEYS-potential-uninitialized-variable.patch

diff --git a/CVE-2016-4470-KEYS-potential-uninitialized-variable.patch b/CVE-2016-4470-KEYS-potential-uninitialized-variable.patch
new file mode 100644
index 0000000..052436d
--- /dev/null
+++ b/CVE-2016-4470-KEYS-potential-uninitialized-variable.patch
@@ -0,0 +1,94 @@
+From edd3cde476d196ebdc771a8fa789d2f4de52ae72 Mon Sep 17 00:00:00 2001
+From: Dan Carpenter <dan.carpenter at oracle.com>
+Date: Wed, 13 Jul 2016 11:43:47 +0100
+Subject: [PATCH] KEYS: potential uninitialized variable
+
+If __key_link_begin() failed then "edit" would be uninitialized.  I've
+added a check to fix that.
+
+This allows a random user to crash the kernel, though it's quite
+difficult to achieve.  There are three ways it can be done as the user
+would have to cause an error to occur in __key_link():
+
+ (1) Cause the kernel to run out of memory.  In practice, this is difficult
+     to achieve without ENOMEM cropping up elsewhere and aborting the
+     attempt.
+
+ (2) Revoke the destination keyring between the keyring ID being looked up
+     and it being tested for revocation.  In practice, this is difficult to
+     time correctly because the KEYCTL_REJECT function can only be used
+     from the request-key upcall process.  Further, users can only make use
+     of what's in /sbin/request-key.conf, though this does including a
+     rejection debugging test - which means that the destination keyring
+     has to be the caller's session keyring in practice.
+
+ (3) Have just enough key quota available to create a key, a new session
+     keyring for the upcall and a link in the session keyring, but not then
+     sufficient quota to create a link in the nominated destination keyring
+     so that it fails with EDQUOT.
+
+The bug can be triggered using option (3) above using something like the
+following:
+
+	echo 80 >/proc/sys/kernel/keys/root_maxbytes
+	keyctl request2 user debug:fred negate @t
+
+The above sets the quota to something much lower (80) to make the bug
+easier to trigger, but this is dependent on the system.  Note also that
+the name of the keyring created contains a random number that may be
+between 1 and 10 characters in size, so may throw the test off by
+changing the amount of quota used.
+
+Assuming the failure occurs, something like the following will be seen:
+
+	kfree_debugcheck: out of range ptr 6b6b6b6b6b6b6b68h
+	------------[ cut here ]------------
+	kernel BUG at ../mm/slab.c:2821!
+	...
+	RIP: 0010:[<ffffffff811600f9>] kfree_debugcheck+0x20/0x25
+	RSP: 0018:ffff8804014a7de8  EFLAGS: 00010092
+	RAX: 0000000000000034 RBX: 6b6b6b6b6b6b6b68 RCX: 0000000000000000
+	RDX: 0000000000040001 RSI: 00000000000000f6 RDI: 0000000000000300
+	RBP: ffff8804014a7df0 R08: 0000000000000001 R09: 0000000000000000
+	R10: ffff8804014a7e68 R11: 0000000000000054 R12: 0000000000000202
+	R13: ffffffff81318a66 R14: 0000000000000000 R15: 0000000000000001
+	...
+	Call Trace:
+	  kfree+0xde/0x1bc
+	  assoc_array_cancel_edit+0x1f/0x36
+	  __key_link_end+0x55/0x63
+	  key_reject_and_link+0x124/0x155
+	  keyctl_reject_key+0xb6/0xe0
+	  keyctl_negate_key+0x10/0x12
+	  SyS_keyctl+0x9f/0xe7
+	  do_syscall_64+0x63/0x13a
+	  entry_SYSCALL64_slow_path+0x25/0x25
+
+Fixes: f70e2e06196a ('KEYS: Do preallocation for __key_link()')
+Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
+Signed-off-by: David Howells <dhowells at redhat.com>
+cc: stable at vger.kernel.org
+Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
+(cherry picked from commit 38327424b40bcebe2de92d07312c89360ac9229a)
+CVE-2016-4470
+Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
+---
+ security/keys/key.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/security/keys/key.c b/security/keys/key.c
+index 2779d13..1d2d3a9 100644
+--- a/security/keys/key.c
++++ b/security/keys/key.c
+@@ -580,7 +580,7 @@ int key_reject_and_link(struct key *key,
+ 
+ 	mutex_unlock(&key_construction_mutex);
+ 
+-	if (keyring)
++	if (keyring && link_ret == 0)
+ 		__key_link_end(keyring, &key->index_key, edit);
+ 
+ 	/* wake up anyone waiting for a key to be constructed */
+-- 
+2.1.4
+
diff --git a/Makefile b/Makefile
index 7936548..933adf9 100644
--- a/Makefile
+++ b/Makefile
@@ -257,6 +257,7 @@ ${KERNEL_SRC}/README ${KERNEL_CFG_ORG}: ${KERNELSRCTAR}
 	cd ${KERNEL_SRC}; patch -p1 < ../kvm-dynamic-halt-polling-disable-default.patch
 	cd ${KERNEL_SRC}; patch -p1 < ../CVE-2016-4794-1-percpu-fix-synchronization-between-chunk-map_extend_.patch
 	cd ${KERNEL_SRC}; patch -p1 < ../CVE-2016-4794-2-percpu-fix-synchronization-between-synchronous-map-e.patch
+	cd ${KERNEL_SRC}; patch -p1 < ../CVE-2016-4470-KEYS-potential-uninitialized-variable.patch
 	sed -i ${KERNEL_SRC}/Makefile -e 's/^EXTRAVERSION.*$$/EXTRAVERSION=${EXTRAVERSION}/'
 	touch $@
 
-- 
2.1.4




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